The invention relates to a storage medium carrying data relating to a plurality of geographical locations, which data comprise for each of the geographical locations a data structure with one or more attribute values.
The invention further relates to a system for reading data relating to a plurality of geographical locations from a storage medium, the data for each of the geographical locations comprising a location code and a data structure with one or more attribute values, which system comprises a read module for reading a given data structure associated with a given location code on the basis of correspondence of a given code to said location code.
The invention further relates to a TMC receiver for receiving traffic messages.
The invention further relates to a method of storing data relating to two or more geographical locations on a storage medium, a data structure with one or more attribute values being stored for each of the geographical locations.
The invention further relates to a system for storing data relating to two or more geographical locations on a storage medium, which system comprises a write module for storing for each of the geographical locations a data structure with one or more attribute values.
The storage and the processing of said data are known from the document "Location Referencing Rules For RDS-TMC", European Road Transport Telematics Implementation Co-ordination Organisation, Task Force on Geographical Location Referencing, CORD Project V 2056, Deliverable No D010, August 995. This document gives a number of rules concerning the specification of geographical locations for use in traffic messages. One application of such traffic messages is the presentation of traffic information to drivers of vehicles. A traffic message is then transmitted from a central station and received by a receiver in the vehicle. Such a receiver is referred to as a Traffic Message Channel (TMC) receiver. This receiver converts the traffic message into information for the driver and reproduces this information via a display screen or via a loudspeaker. The data specifying a geographical location is stored on a local storage medium in a system in the receiver. A traffic message generally includes only a reference to a geographical location and upon reception of the traffic message the system in the vehicle retrieves the data relating to the geographical location from the local storage medium. Page 22 of the reference specifies a number of location types. For each of said types it is defined which attributes, i.e. what types of data, form the specification. Some attributes are mandatory and some are optional. In addition to said attributes, it is further possible to include extra attributes in order to adapt the specification of geographical locations to a given application, see for example pages 27 and 28 of the reference. Annex A1 of the reference contains a more comprehensive list of types of geographical locations.
The known system, which utilizes information about geographical locations in the above manner, carries the data relating to a multitude of geographical locations on a local storage medium. For each geographical location space for any possible attribute of a geographical location has been reserved on the storage medium. This results in a record having a fixed layout in fields which store values of the attributes. The system knows this layout and consequently knows the location in the record where the value of a given attribute is stored, for example the name or the number of a road, and can process this information. A drawback of the known storage medium is that some of the fields reserved in the records on the storage medium remain unused because no values exist for all the possible attributes of each geographical location. A further drawback of the known storage medium is that a future extension of attributes of a geographical location makes it necessary for the system reading the storage medium to be immediately adapted to the extension. A new version of the storage medium storing records with a new field for a new attribute cannot be read by the current version of the system because the layout of the record has been changed.